It is well documented that atrial fibrillation (AF), either alone or as a consequence of other cardiac disease, continues to persist as the most common type of cardiac arrhythmia. In the United States, AF currently affects an estimated two million people, with approximately 160,000 new cases being diagnosed each year. The cost of treatment for AF alone is estimated to be in excess of $400 million worldwide each year
Although pharmacological treatment is available for AF, the treatment is far from perfect. For example, certain antiarrhythmic drugs, like quinidine and procainamide, can reduce both the incidence and the duration of AF episodes. Yet, these drugs often fail to maintain sinus rhythm in the patient. Cardioactive drugs, like digitalis, Beta blockers, and calcium channel blockers, can also be given to control AF by restoring the heart's natural rhythm and limiting the natural clotting mechanism of the blood. However, antiarrhythmic drug therapy often becomes less effective over time. In addition, antiarrhythmic drug can have severe side effects, including pulmonary fibrosis and impaired liver function.
Another therapy for AF is surgery. In a technique known as the “Maze” procedure, a surgeon makes several incisions through the wall of the atrium with a scalpel and then sews the cuts back together, creating a scar pattern. The scars isolate and contain the chaotic electrical impulses to control and channel the electrical signals. The Maze procedure is expensive, complicated to perform, and associated with long hospital stays and high morbidity.
An alternative to open heart or open chest surgery is a minimally invasive “cryo-maze” procedure in which a cryosurgical catheter is used to form ablative scars in various locations in the atrial tissue. This method creates the same scar pattern more easily than the “Maze” procedure and leaves the connective tissue intact as opposed to cutting it. The cryosurgical catheter includes a handle, a highly flexible shaft, and a flexible thermally-transmissive region, where the handle, the shaft, and the thermally-transmissive region define a fluid pathway which is in fluid communication with the fluid supply. The cryogenic fluid can be in a liquid or a gas state. An extremely low temperature can be achieved within the catheter, and more particularly on the surface of the catheter by cooling the fluid to a predetermined temperature prior to its introduction into the catheter or, alternatively, by using Joule-Thomson expansion of the cooling gas in the thermally-transmissive region. The catheter is then introduced into the patient and the thermally-transmissive region contacts the area of the heart where the surgeon desires to form scar tissue.
However, a significant problem with cryosurgical catheters is that when extreme cold is applied to the heart tissue the thermally-transmissive region adheres to the tissue and the surgeon must apply warm saline other fluid to release it. This necessarily results in an extended procedure time because first, warm fluid needs to be applied to the surgical site and then excess fluid must be manually suctioned from the patient. In addition, the extended procedure time presents possible risk to the patient as the patient prolongs the period of time spent under anesthesia.
Thus, it would be desirable to provide a catheter having an internal source of warming fluid to enable the surgeon to quickly and easily thaw the thermally-transmissive region of the catheter.